System Aims to Concentrate Power of 2000 Suns

Photonics.comApr 2013
ZURICH, April 22, 2013 — A photovoltaic system capable of harnessing the power of 2000 suns and converting 80 percent of incoming light into useful energy could provide sunny, remote locations with electricity, fresh water and cooler air at lower prices than conventional devices.

It would only take 2 percent of the solar energy from the Sahara Desert to supply the world’s electricity needs, according to a study from the European Solar Thermal Electricity Association and Greenpeace International. However, current solar technologies are too expensive and slow to produce, require rare-earth minerals, and lack the efficiency to make such massive installations practical.

Now an international collaboration of scientists from IBM Research, ETH Zurich, both of Zurich, Airlight Energy of Biasca and Interstate University of Applied Sciences Buchs NTB of St. Gallen have developed a lower-cost solution to harness the power of 2000 suns; funding will be under a three-year, $2.4 million grant from the Swiss Commission for Technology and Innovation. The high-concentration photovoltaic thermal (HCPVT) system features an inexpensive design and achieves a cost-per-aperture-area less than $250 per square meter — three times lower than comparable systems — and a levelized cost of energy less than 10 cents per kilowatt-hour.

Rendering by Airlight Energy of the prototype HCPVT system under development by an international collaboration of researchers. The prototype system uses a large parabolic dish — made from a multitude of mirror facets — that is attached to a tracking system that determines the best angle based on the position of the sun. Once aligned, the sun’s rays reflect off the mirror onto several microchannel-liquid cooled receivers with triple-junction photovoltaic chips; each 1 x 1-cm chip can convert 200-250 W, on average, over a typical 8-hour day in a sunny region. The entire receiver combines hundreds of chips and provides 25 kW of electrical power. Images courtesy of IBM Research.
The prototype HCPVT system uses a large parabolic dish composed of many mirror facets that are attached to a sun-tracking system, which positions the dish at the best angle to capture the sun’s rays. The rays are reflected off the mirrors onto several microchannel-liquid cooled receivers with triple-junction photovoltaic chips — each 1 x 1-cm chip can convert between 200 and 250 W, on average, over a typical 8-hour day in sunny locations.

“We plan to use triple-junction photovoltaic cells on a microchannel cooled module which can directly convert more than 30 percent of collected solar radiation into electrical energy and allow for the efficient recovery of an additional 50 percent waste heat,” said Bruno Michel, manager of advanced thermal packaging at IBM Research. “We believe that we can achieve this with a very practical design that is made of lightweight and high-strength concrete, which is used in bridges, and primary optics composed of inexpensive pneumatic mirrors — it's frugal innovation, but builds on decades of experience in microtechnology.”

The entire receiver combines hundreds of chips to provide 25 kW of electrical power. The photovoltaic chips are mounted on microstructured layers that pipe liquid coolants within a few tens of micrometers off the chip to absorb the heat and draw it away 10 times more effectively than with passive air cooling. The coolant maintains the chips at almost the same temperature for a solar concentration of 2000 times and can keep them at safe temperatures up to a solar concentration of 5000 times.

The direct cooling solution with very small pumping power was inspired by the hierarchical branched blood supply system of the human body and has been tested by IBM scientists in high-performance computers, including Aquasar. An initial demonstrator of the multichip receiver was developed in a previous collaboration between IBM and the Egypt Nanotechnology Research Center.

A prototype of the HCPVT is currently being tested at the IBM Research lab in Zurich. Several prototypes of the HCPVT system will be built up in Biasca and Rüschlikon, Switzerland, as part of this collaboration. The direct cooling solution with very small pumping power is inspired by the hierarchical branched blood supply system of the human body and has been already tested by IBM scientists in high-performance computers, including Aquasar. An initial demonstrator of the multichip receiver was developed in a previous collaboration between IBM and the Egypt Nanotechnology Research Center.
"The design of the system is elegantly simple,” said Andrea Pedretti, chief technology officer at Airlight Energy. “We replace expensive steel and glass with low-cost concrete and simple pressurized metallized foils. The small high-tech components, in particular the microchannel coolers and the molds, can be manufactured in Switzerland with the remaining construction and assembly done in the region of the installation. This leads to a win-win situation where the system is cost-competitive and jobs are created in both regions.”

ETH Zurich will develop the solar-concentrating optics.

“Advanced ray-tracing numerical techniques will be applied to optimize the design of the optical configuration and reach uniform solar fluxes exceeding 2000 suns at the surface of the photovoltaic cell,” said ETH Zurich professor Aldo Steinfeld.

Fresh Water and Cool Air
Current concentration photovoltaic systems collect electrical energy and dissipate thermal energy into the atmosphere. The HCPVT system aims to eliminate the overheating problems of solar chips while also repurposing the energy from thermal water desalination and adsorption cooling.

To capture the medium-grade heat, IBM engineers used an advanced technology developed for water-cooled high-performance computers such as Aquasar and SuperMUC to absorb heat from the processor chips. This heat was repurposed to provide space heating for the facilities.

The prototype system under development. The photovoltaic chips are mounted on microstructured layers that pipe liquid coolants within a few tens of micrometers off the chip to absorb the heat and draw it away 10 times more effectively than with passive air cooling.
Instead of heating a building, the system’s 90 °C water will be used to heat salty water, which will be passed through a porous membrane distillation system where it is vaporized and desalinated. This process could provide 30 to 40 liters of drinkable water per square meter of receiver area per day while generating electricity with a more than 25 percent yield, or 2 kilowatt-hours per day — a little less than half the amount of water the average person needs per day, according to the United Nations. A larger installation could provide enough water for a town.

The system also could provide air conditioning by means of a thermal-driven adsorption chiller. Such devices, with water as working fluid, could replace compression chillers, which stress electrical grids in hot climates and contain working fluids that are harmful to the ozone layer.

The HCPVT solution could provide sustainable energy and potable water to locations around the world, including southern Europe, Africa, South America, Australia, the Arabic peninsula and the southwestern US, the scientists say. It could also find use in remote tourism locations on small islands like the Maldives, Seychelles and Mauritius, since conventional systems require separate units, with consequent loss in efficiency and increased cost.

A prototype of the HCPVT system is now being tested at IBM Research-Zurich. Additional prototypes will be built in Biasca and Rüschlikon, Switzerland, as part of the collaboration.